In recent years, lipid intake has been increasing in Japan with the tendency toward improved and Western-style eating habits, which brings about a problem of excessive fat intake. The excessive fat intake causes obesity and an increase in the serum lipid level and consequently heightens the risk of the onset of various complications thereof (for example, circulatory diseases, in particular, coronary and cerebral vascular accidents and life-style related diseases such as certain cancers including breast cancer and colon cancer). Thus, it becomes a serious social problem from the viewpoint of maintaining and improving national health.
It has been pointed out that an increase in the levels of cholesterol in the blood is one of the risk factors of the onset of circulatory diseases. Recently, high concentrations of triacylglycerol (triglyceride) in the blood have also attracted attention as another risk factor independent from those of cholesterol.
Hyperlipemia means a condition wherein the blood cholesterol concentration and/or the blood triacylglycerol (i.e., one of neutral fats) concentration are increased. Hypercholesterolemia (hyper-β-lipoproteinemia) with an increase in the blood cholesterol level is caused mainly by an increase in the low-density lipoprotein (LDL, β-lipoprotein) to a level which is well known as one of the risk factors for atherosclerosis. It is also pointed out that the excessive lipid intake results in a continuous increase in the blood triacylglycerol concentration and, in turn, causes the onset of hypertriacylglycerolemia which is likely to induce atherosclerotic diseases such as hypertension and ischemic heart disease.
Moreover, an excess in stored energy due to the excessive lipid intake causes obesity. Obesity, which is defined as a condition with an abnormal increase in adipose in the body, is associated with an increase in visceral adipose and/or panniculus adipose. Classifications of obesity are: obesity in the upper half of the body; obesity in the lower half of the body; central obesity; peripheral obesity; visceral obesity; panniculus obesity and the like depending on the part of the body with the increased amount of adipose.
Also, obesity is regarded as one of the causative factors of life-style related diseases such as diabetes, hyperlipemia, hypertension, fatty liver, atherosclerosis, gout, myocardial infarction and angina. People suffering from these diseases sometimes develop complications depending on the areas of adipose deposition. It has been recently clarified that visceral adipose deposition is associated with the highest risk.
Methods of treating hyperlipemia and obesity include dietotherapy and chemotherapy which are usually combined with kinesitherapy and health guidance. However, these existing therapies suffer from various drawbacks: it is highly difficult to continue these treatments over a long period of time; they are less convenient; and there is a fear of side effects.
The percentage of patients with atherosclerosis in the total population of Japan has been increasing constantly and it is known that abnormal lipid metabolism is deeply involved in the formation of atherosclerosis.
It has been known that valine, which is one of the essential amino acids, is usable in therapeutic agents for liver regeneration (WO96/00059) and therapeutics for hepatic diseases (WO99/16433). However, it has neither been reported nor suggested so far to use valine in improving lipid metabolism or preventing, ameliorating or treating hyperlipemia, obesity or atherosclerosis.